CV-18 Fujian/003 CATOBAR carrier thread

[Max Demian]

Would not a steam catapult imply steam turbine propulsion?

The 60MW figure for EMALS is all over the internet.

Would've been nicer if you could've pointed me to a peer-review source. But I did some search of my own. One source I found (1995) claims that steam catapults have an operational energy limit of 95 MJ. The same paper provides a figure with tow force over time, peaking at about 210 kilopounds, or 930 kN. Given a catapult cylinder length of 101m, that comes up to 94MJ, which sounds consistent. Again, taking the 2.8 second launch time, we get 34 MW power for the steam catapult.

For the EMALS the source states a 122 MJ launch energy, or 43.5 MW average power. Now for the actual input power, I couldn't find a clear number. The source mentions that 4 flywheels will be necessary, each with a peak power of 81.6 MW and 121MJ of energy storage. So by that logic, no sane number of gas turbines could meet the instantaneous power requirements.

Compare this to the steam catapult: the authors mention that the steam catapult is only 5% efficient? This would imply 1.9 GJ of required input energy per launch.

 

[Intrepid]

What is the difference between steam-driven (oil or nuclear fired) or gasturbine-driven generators? Does a carrier needs different types of flywheels depending on the source driving the generators?

 

[Max Demian]

What is the difference between steam-driven (oil or nuclear fired) or gasturbine-driven generators? Does a carrier needs different types of flywheels depending on the source driving the generators?

The flywheels considered for EMALS are electric powered, so independent of the power generation system.

 

[Intrepid]

The flywheels considered for EMALS are electric powered, so independent of the power generation system.

So regardless of nuclear-fired-boilers, oil-fired-boilers, gasturbines or dieselengines, you need generators and flywheels for the electromagnetic catapults. If you have more powerfull generators, you can fire every 15 seconds an aircraft into the sky. And if you have less powerfull generators, you can fire every 60 seconds or every two minutes. That is the difference?

A Ford-Class aircraft carrier has three sets of four flywheels to switch them between the four catapults. One set of four flywheels for one catapult as testet in Lakehurst is ready for use, but with three sets (together 12 flywheels) for four catapults the switching device has still problems.

 

[Max Demian]

So regardless of nuclear-fired-boilers, oil-fired-boilers, gasturbines or dieselengines, you need generators and flywheels for the electromagnetic catapults. If you have more powerfull generators, you can fire every 15 seconds an aircraft into the sky. And if you have less powerfull generators, you can fire every 60 seconds or every two minutes. That is the difference?

That's my understanding, yes. The paper I quoted mentioned a 45s cycle time requirement for EMALS. This could be met with an average electric power input of only 6.35 MVA.

 

[Intrepid]

That's my understanding, yes. The paper I quoted mentioned a 45s cycle time requirement for EMALS. This could be met with an average electric power input of only 6.35 MVA.

I am not familiar with MVA. Can you give me an example, what installation this requirement meets?

 

[delft]

I am not familiar with MVA. Can you give me an example, what installation this requirement meets?

MVA = mega volt ampere = mega watt = MW.
I'm pretty sure that the efficiency of an EM cat system, from high pressure steam to electrical generator to storage device to the actual EM cat is better than 5%.

 

[Intrepid]

MVA = mega volt ampere = mega watt = MW.

This means that the

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needs five instead of four diesel generators if it is equipped with electromagnetic catapults?

 

[Max Demian]

MVA = mega volt ampere = mega watt = MW.
I'm pretty sure that the efficiency of an EM cat system, from high pressure steam to electrical generator to storage device to the actual EM cat is better than 5%.

The paper estimated a 70% efficiency for the catapult itself, and peak loss of 13.3 MW in the stator, necessitating active cooling. Thermal power to electrical power will be < 50% efficient. Energy efficiency of flywheels (energy in / energy out) can be as high as 90%. So rough estimate for your example, with a steam turbine generator: 0.4*0.7*0.9=25.2%

 

[Max Demian]

This means that the

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needs five instead of four diesel generators if it is equipped with electromagnetic catapults?

You would need about 25MW continuous power for 4 catapults. The 4 diesel generator of QE class would seem sufficient (40MW combined). However, keep in mind that when launching aircraft, the carrier is operating at near flank speed and in case of QE with IEP would have less spare power available. So, I don't how that would affect the overall power budget - depends on how much over provisioning they have in place right now.